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Re: Help with WV_CWT [message #81680 is a reply to message #81654]

Mon, 08 October 2012 18:25

Phillip M. Bitzer
Messages: 7
Registered: September 2012

Junior Member

Balt-

AFAIK, there is no "simple" connection between frequency and scale. It's
not quite as simple as an FFT (although you might argue to ordering of
frequencies returned by IDL isn't exactly simple :-) )

There are a couple things to help you along. First, the IDL Wavelet
toolkit helped me a lot when learning about wavelets:

vis.lbl.gov/NERSC/Software/idl/help/docs6.0/wavelet.pdf

I also suggest you take a peek at the site:

http://paos.colorado.edu/research/wavelets/

Chis Torrence wrote most (all?) of the wavelet routines for IDL. The
article "A Practical Guide to Wavelet Analysis" he is lead author on is
quite useful.

For the immediate problem of how scale relates to frequency, check out
this from the aforementioned web site:

The period (or inverse frequency) is the approximate Fourier period that
corresponds to the oscillations within the wavelet. For all wavelets,
there is a one-to-one relationship between the scale and period. The
relationship can be derived by finding the wavelet transform of a pure
cosine wave with a known Fourier period, and then computing the scale at
which the wavelet power spectrum reaches its maximum.

http://paos.colorado.edu/research/wavelets/faq.html#scale

I recall that I mucked around a lot "under the hood" with the wavelet
routines to really understand them. I also use wv_applet quite a bit to
check my own code.

Hope this helps!

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[Message index]

		Re: Help with WV_CWT By: Balthasar Indermuehle on Thu, 11 October 2012 19:38
		Re: Help with WV_CWT By: Phillip M. Bitzer on Mon, 08 October 2012 18:25
		Re: Help with WV_CWT By: Michael Galloy on Mon, 08 October 2012 15:53
		Re: Help with WV_CWT By: Balthasar Indermuehle on Mon, 08 October 2012 15:38

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